1. Field of the Invention
The present invention relates to pulp and paper making apparatus and in particular to pressurized disc-type refiners for reducing wood chips and like materials to pulp.
2. Brief Description of the Prior Art
One type of apparatus used in the production of wood pulp is the so called pressurized disc-type refiner. In this type of apparatus a pair of opposed parallel discs having attrition elements on their adjacent faces are adapted for relative rotation with respect to each other and are enclosed in a pressurized housing. The discs may each to be rotated in opposite directions, or one disc may be fixed while the other is rotated.
Wood chips or like material to be refined are usually introduced between the plates at their centers and are refined by being advanced across the closely spaced attrition elements by centrifugal force and generated steam. Free steam is generated by this refining process, and adjacent to the outer peripheral edge of the discs the refined material is discharged along with this steam through a port in the refiner.
This steam is typically at a pressure from about 15 to 200 pounds per square inch. Thus, it may be used for a number of heating purposes in the paper mill such as for heating the drying rolls on a paper machine. It is, of course, necessary that this high pressure steam be separated from the reduced fibrous material before it can be used in this manner, and several devices are presently in use for this purpose. Centrifugal devices such as a standard centrifugal cyclone are, for example, commonly employed to effect such separation. In an alternative kinetic energy device, a fan impellar enclosed in a pressurized housing throws the heavier fibrous material to the outer perimeter of the housing from where it is then discharged. The lighter steam recovered passes through the center of the housing from where it is recovered for use elsewhere in the paper will.
It will be appreciated that the above described means for separating steam from fibrous material require certain auxiliary equipment which may be costly both in terms of its initial procurement and the plant space which it then consumes. It is, therefore, the object of the present invention to provide a means for separating high pressure steam from fibrous material which avoids these disadvantages.